The Internet provides a versatile communication channel for various machines, or communication devices, to communicate with each other. Many applications have been developed to use the Internet to meet various communication needs.
For example, electronic mails (emails) are electronic files that can be transferred from one computer to another over the Internet. For reliable transmission, emails may be queued at various stages of the transmission from the originating computer to the destination. For example, an outgoing email may be queued in a mail server until a communication connection can be made to transfer the email. Typically, incoming emails are queued in the inbox of the computer, waiting for the user to view.
Instant messaging (IM) provides convenient two-way real-time communication between people using a variety of different device types, such as a personal computer (PC), a personal digital assistant (PDA), a digital cellular phone, etc. Instant messaging can incorporate image, voice and/or video. Instant messages are transmitted in a real time fashion over a communication connection between two devices for an instant messaging session. When the communication connection breaks, the instant messaging session ends. For example, when one of the devices used in the instant messaging session shuts down (or restarts, goes offline, etc.), the instant messaging session ends.
Currently, there are a number of instant messaging systems available, such as Google's Hello, American Online Instant Messenger (AIM), Microsoft Network (MSN) messenger, Java Instant Messaging, Jabber, ICQ, etc.
Most messaging systems allow users to connect to each other according to user identities. A user can have a contact list of user identities as friends or a buddy list. The messaging system provides services for the users to connect to each other according to the user identities.
Many messaging systems provide services for user presence information. In a traditional messaging system, presence awareness lets users know whether other users, particularly those on their contact lists, are on-line and willing to accept messages.